1. Field of the Invention
This invention relates to a magnetoresistive (MR) head of the type wherein an elongated thin film is brought into direct contact with a recording medium, and, in response to signals recorded in the medium, signal current flowing the length of the film is caused to vary. More particularly, however, the invention relates to an improved form of MR head of the "non-shunt bias" type . . . which head is characterized by especially long life.
2. Description Relative to the Prior Art
Shunt biased MR heads are well known to the art. C. D. Mee and Eric Daniel, in their recent book "Magnetic Recording", McGraw Hill Inc., 1987, page 290, FIG. 4.33 describe a shunt biased MR head. In their depiction, an electrically conductive layer is indicated as running parallel to the length of an MR strip, such conductive layer being so disposed that, when carrying a current therethrough, it creates an encircling magnetic field about the conductive layer which exerts a bias against the magnetic moment associated with the MR strip. The electrically conductive layer in a shunt biased MR head may be of any convenient form; and, indeed, chromium, titanium, and other metallic layers have been employed for current shunting purpose, all such layers being however sufficiently thick so as to exhibit low sheet resistance to the flow of bias-producing shunt current. Typically, a shunt bias layer is as thick as, or thicker than, an MR strip with which it cooperates.
A problem associated with any MR head concerns the matter of corrosion associated with the MR strip, i.e. the strip being typically comprised of nickel iron (NiFe) permalloy, it is subject to the deleterious effects of electrochemical attack.
It has long been known, say, in the protection of
1. the hull and propeller of a ship from corrosion to strategically place a chemically more active (i.e. according to the electrochemical series) "sacrificial" material, such as zinc, in proximity to the hull and propeller, thereby to "anodically" corrode away the zinc instead of the steel and brass of which the hull and propeller are made, and
2. the use of sacrificial bars of, for example, magnesium in proximity to underground pipes and cables to protect such pipes and cables from corrosion, the magnesium being in such case the preferntial element of anodic decay.
See "Principles and Applications of Electrochemistry" by W. A. Koehler, John Wiley and Sons Inc., New York, page 364 et seq.
(As is known, for sacrificial protection to work, electrical conductivity must exist between the sacrificial conductor and the component being protected.)